Thermoset resins are materials that cure to form very hard plastics. These materials can be used in a wide variety of consumer and industrial products. For example, thermosets are used in protective coatings, adhesives, electronic laminates (such as those used in the fabrication of computer circuit boards), flooring and paving applications, glass fiber-reinforced pipes, and automotive parts (including leaf springs, pumps, and electrical components). Relative to other types of plastics, cured thermosets are typically brittle. Addition of a poly(arylene ether) to a curable thermoset composition is known to decrease the brittleness of the cured resin.
When the thermoset resin is an epoxy resin or other resin reactive with phenolic hydroxy groups, the poly(arylene ether) is typically “unfunctionalized” in the sense that it possesses one or more terminal hydroxy groups that are present in the poly(arylene ether) as synthesized by oxidative polymerization of a phenol compound. When the thermoset resin comprises reactive carbon-carbon double bonds or triple bonds (as, for example, in (meth)acrylate resins, vinyl resins, unsaturated polyesters, and the like), the poly(arylene ether) is typically functionalized with groups that can be copolymerized with the reactive carbon-carbon double bonds or triple bonds of the resin. As used herein, the prefix “(meth)acryl” means acryl- or methacryl-.
Poly(arylene ether)s are often produced by oxidative polymerization of a monohydric phenol, optionally in the presence of a polyhydric phenol, in a good solvent for the product poly(arylene ether). Various techniques of isolating poly(arylene ether)s from solution have been described. Some poly(arylene ether)s have been isolated from solution by precipitation in an antisolvent, such as methanol. However, such precipitation methods often produce poor yields of poly(arylene ether)s with low molecular weight and/or high relative concentrations of phenolic hydroxy groups. Some poly(arylene ether)s have been isolated by a so-called devolatilizing extrusion process in which heat and reduced pressure in an extruder are used to drive off solvent. See, for example, U.S. Pat. Nos. 6,211,327 B1 and 6,307,010 to Braat et al. However, some poly(arylene ether)s undergo thermal and/or oxidative degradation in these devolatilizing extrusion processes. Furthermore, when some low molecular weight poly(arylene ether)s are extruded as strands and cooled in a water bath, the strands will occasionally break, causing an inconvenient interruption in the process. In addition, devolatilizing extrusion is considered unsuitable for isolating poly(arylene ether)s functionalized with polymerizable groups, which may react under the extrusion conditions to form a crosslinked polymer.
There is therefore a need for a method of separating a poly(arylene ether) from solvent that is generally adaptable to a variety of unfunctionalized and functionalized poly(arylene ether)s of various molecular weights.